All things considered though, none of the Kami Trio (that's what Landorus/ Tornadus/ Thundurus are called) should outspeed a +1 Sharpedo with max speed EVs unless they're scarfed. You could also be facing Prankster Tornadus/ Thundurus, in which case that would explain why your +1 Sharpedo is being out sped.

The problem with both Mamo & Weavile is that they're also weak to fighting & grass/ fighting, bug & fairy. In terms of synergy, you should remember to cover those weaknesses with the rest of your team.

At the top of my head I can only think of one. (Then again I'm up at 4 AM writing this xD)

Mamoswine

It can practically kill them all with a physical Ice type attack. That or force your opponent to switch into someone else. Though Ice Shard should get the job done. If you set up Stealth Rocks then you can try to stall them out through that.

They are all Flying types.
Landorus is Ground-Flying, Thundurus is Electric-Flying, and Tornadus is pure Flying.

Flying is weak to Rock, Electric, and Ice.

Electric is a bad counter right off the bat due to Landorus' Ground Type.
Rock is okay but it only does x1 Damage to Landorus, who seems to be the most common of the three.Ice, however, is your best bet. 4x Damage to Landorus, 2x damage to the other two.A fast Ice type counters all 3 nicely. A nice fast Ice Type you can use is Weavile.

Even though it has its fair share of weaknesses, 120 Attack and 125 Speed with a STAB Ice Punch will make Landorus faint and inflict serious damage on the others. The other moves are for coverage. Pressure runs down PP, Pickpocket steals items and can disrupt strategies.